Roadway repair is often accomplished by overlaying the existing pavement (whether of concrete or asphalt composition) with a new layer (often called a leveling course) of concrete, asphalt or other surfacing materials. Without prior surface treatment, however, this method of repair generally results in the application of insufficient quantities of paving material in the rutted, potholed or otherwise damaged areas, because the overlay will be applied at the same rate per unit of roadway width in damaged areas (which have a greater depth across the width) as in the undamaged areas. The resulting reduced density in the overlay of the previously damaged areas will lead to renewed rutting or other wear damage in the new pavement in relatively short order. However, by milling the surface of the damaged pavement to an elevation below the level of damage, newly added pavement will have a uniform thickness across the entire width of the roadway. In addition, a repaving technique that includes milling a thickness of old pavement and replacing it with an equivalent thickness of new pavement will return the elevation of the roadway to its initial level, whereas the placement of a leveling course atop damaged pavement will tend to raise the surface of the roadway or some portion thereof above its original elevation. This can require the raising of road shoulders, guardrails and manhole covers and the adjustment of overpass clearances, all of which will be unnecessary if a proper milling technique is employed. A use of milling prior to repaving can also permit ready establishment of the proper road grade and slope, and thereby avoid drainage and safety problems. Furthermore, milling typically provides a rough surface that readily accepts and bonds with the new asphalt or other pavement overlay. Finally, milling can provide raw material that can be reclaimed for use in the production of new paving materials.
A milling machine typically comprises a wheeled or track-driven vehicle that includes a rotating cutter drum on which are mounted a plurality of cutting teeth. This cutter drum is mounted in a housing on the frame of the machine and is adapted to be lowered into contact with the road surface and rotated about a horizontal axis so as to cut into the surface to a desired depth as the machine is advanced along the roadway. The cutter drum is rotated by a primary drum drive assembly typically comprising a drive belt driven by a diesel engine, which drive belt engages a sheave on an input drive shaft for the cutter drum. A gear box is typically located between the sheave and the cutter drum and includes a gear train and an output drive shaft on which the cutter drum is rotated. The gear box thus allows for rotation of the output drive shaft for the cutter drum at a speed and torque that is different from that of the input drive shaft. Generally, the milling machine also includes a conveyor system that is designed to carry the milled material that has been cut from the roadway by the rotating cutter drum to a location in front of, to the rear of or beside the machine for deposit into a truck for removal from the milling site. Steerable track or wheel drive assemblies typically operated by hydraulic or electric motors are provided to drive the machine and to steer it along a desired milling path. Power for operation of the hydraulic motors that are typically employed to operate the conveyors and the drive assemblies is usually provided by the diesel engine.
A road stabilizer is similar to a milling machine in that it comprises a wheeled or track-driven vehicle that includes a rotating cutter drum on which are mounted a plurality of cutting teeth, which drum is rotated by a primary drum drive assembly typically comprising a belt drive that engages a sheave on an input drive shaft for the cutter drum. A gear box is typically located between the sheave and the cutter drum and includes a gear train and an output drive shaft on which the cutter drum is rotated. The gear box thus allows for rotation of the output drive shaft for the cutter drum at a speed and torque that is different from that of the input drive shaft. However, the cutter drum of a road stabilizer is generally employed to mill or pulverized an existing road bed or roadway to a greater depth than does a milling machine prior to repaving (usually called reclaiming) or prior to initial paving (usually called stabilizing), and it leaves the pulverized material in place. The pulverized material left behind is usually compacted and covered with one or more additional layers of crushed aggregate material before paving.
Cold in-place recycling (“CIR”) machines can be used to repair damage to a roadway in a single pass, while reusing essentially all of the existing asphalt paving material. In the CIR process, damaged layers of asphalt pavement are removed. The removed material is processed and replaced on the roadway and then compacted. If a roadway has good structural strength, CIR can be an effective treatment for all types of cracking, ruts and holes in asphalt pavement. CIR can be used to repair asphalt roadways damaged by fatigue (alligator) cracking, bleeding (of excess asphalt cement), block cracking, corrugation and shoving, joint reflective cracking, longitudinal cracking, patching, polished aggregate, potholes, raveling, rutting, slippage cracking, stripping and transverse (thermal) cracking. CIR can almost always be used when there is no damage to the base of the roadway. Generally, CIR is only half as expensive as hot mix asphalt paving while providing approximately 80% of the strength of hot mix asphalt paving. CIR can be carried out with the aid of a milling machine or a road stabilizer/reclaimer machine that has been modified by mounting an additive spray bar in the cutter drum housing to inject an asphalt emulsion or foamed asphalt cement additive into the cutter drum housing. The asphalt emulsion or foamed asphalt cement additive is then thoroughly blended with the milled material by the cutter drum and can be left in a windrow or fed by the CIR machine's discharge conveyor directly into an asphalt paving machine. Generally, the additive material is supplied from a separate additive supply tank truck that is coupled to the modified milling machine or road stabilizer/reclaimer machine. The additive material is drawn directly from the tank on the additive supply truck and metered through an additive flow system that is mounted on the milling machine to the spray bar in the cutter drum housing.
Because the cutter drums of a conventional milling machine, a conventional road stabilizer and a milling machine or road stabilizer used in a CIR process operate in the same way for purposes of this invention, the term “milling machine” will be used hereinafter as a generic term that describes all three types of machines.
The cutting teeth on the cutter drum of a milling machine are subjected to significant wear forces as the milling, reclaiming, stabilizing or recycling process is carried out. These cutting teeth will break or become dull with use and must be periodically replaced. Consequently, it is necessary to inspect the cutter drum on a regular basis to determine if cutting teeth need to be replaced, to replace them, and to detect and repair any damage that has been incurred by the cutter drum. However, it is hazardous for maintenance personnel to get close enough to the cutter drum for inspection while the primary drum drive assembly for the milling machine is operating, or while the cutter drum is being rotated at any significant speed, because of the risk of injury due to proximity to the rotating drum. Furthermore, the cutter drum is generally rotated by the primary drum drive assembly at a speed that is too fast, even when the engine is throttled down, to allow any meaningful inspection of the cutter drum by maintenance personnel. Attempts to “bump” the rotation circuit of the primary drum drive assembly at engine idle speed in order to facilitate inspection may result in over-rotation that is not useful for inspection or uncontrolled rotation of the cutter drum that can ensnare the clothing of maintenance personnel on the cutting teeth within the drum housing.
Attempts have been made to rotate the cutter drum by hand with the power supply to the primary drive assembly of the cutter drum turned off, but the belt drive assembly, gearbox and other components of the typical primary drive assembly produce large frictional forces which must be overcome. Furthermore, the cutter drum of a milling machine is massive and heavy, and it requires considerable torque to move it.
Conventional systems are known for providing separate drive assemblies that operate on or through components of the primary drive assembly for the cutter drum. Thus, for example, U.S. Pat. Nos. 7,644,994, 8,167,378, 8,480,181, 8,807,662, 9,512,576 and 9,624,628 all describe auxiliary drive assemblies that operate by engaging one or more components of the primary drive assembly for the cutter drum. U.S. Pat. Nos. 8,905,488 and 9,016,800 describe an auxiliary drive assembly having a separate belt drive assembly that cooperates with components of the primary drum drive assembly to rotate the cutter drum.
All of these conventional systems operate with the primary drive assembly operatively attached to the cutter drum. Furthermore, all of these conventional auxiliary drive assemblies require cooperation with at least some of the components of the primary drive assembly. It would be desirable if a mechanism could be provided for disengaging the primary drive assembly from the cutter drum in order to prevent accidental or inadvertent rotation of the cutter drum by the primary drum drive assembly. It would also be desirable if a mechanism could be provided that would allow for rotation of the cutter drum through a small angle of rotation without having to overcome the large frictional forces inherent in the primary drive assembly. It would also be advantageous if an auxiliary drive assembly could be provided that is independent of the primary belt drive assembly.